It has become common to treat a variety of medical conditions by temporarily or permanently introducing a coated medical device, and, in particular, a coated medical implanted device partly or completely into the esophagus, trachea, colon, biliary tract, urinary tract, vascular system or other location within a human or veterinary patient. Many treatments of the vascular or other systems entail the introduction of a device such as a stent, a catheter, a balloon, a wire guide, a cannula or the like. For this purpose, a stent may most simply be considered as a cylinder of relatively short length which opens a body passage or lumen or which maintains a body passage or lumen in an open condition. In addition, balloons such as angioplasty or dilation balloons may be advanced into the human or veterinary patient and then expanded to open the body passage or vessel lumen.
Such medical devices are generally capable of serving their intended purposes quite well. Some drawbacks can be encountered during their use, however. For example, when a balloon is expanded to open a body passage or vessel lumen, the expanded balloon may cause potential trauma or injury to the expanded passage or vessel. Likewise, when a device is introduced into and manipulated through the vascular system of a patient, the blood vessel walls can be disturbed or injured. Clot formation or thrombosis often results at the injured site, causing stenosis (closure) of the blood vessel. Moreover, if the medical device is left within the patient for an extended period of time, thrombus can form on the device itself, again causing stenosis. As a result, the patient is placed at risk of a variety of complications, including heart attack, pulmonary embolism, and stroke. Thus, the use of such a medical device can entail the risk of precisely the problems that its use was intended to ameliorate.
When medical devices such as stents and, in particular, coated stents are implanted in a vessel lumen, edge effect trauma can occur to the tissue at and beyond the ends of the implanted stent. This trauma or injury can be the result of the implanted stent causing injury to the vessel wall. However, delivery of such an implanted stent normally includes the use of an inflatable balloon on which the stent is mounted with the ends of the balloon extending axially beyond the ends of the stent. When the balloon is inflated to deliver the stent, the ends of the balloon extending beyond that of the stent inflate so as to dilate and injure the tissue extending beyond the ends of the stent. Should the stent be coated or include a therapeutic agent, the therapeutic agent can possibly cause injury to the tissue extending beyond the ends of the stent. This therapeutic agent or treatment could include a chemical, radiation, or biochemical agent or other type of treatment. Furthermore, delivery agents such as polymers and the like used to deliver the treatment agent can also cause this edge effect reaction to the tissue extending beyond the ends of the implanted stent. However, it is to be understood that regardless of the cause of the trauma or injury to the vessel wall, the tissue will typically react with the proliferation of smooth muscle cells and the like, thereby creating an adverse reaction and subsequent closure or stenosis of the vessel.
Another way in which blood vessels undergo stenosis is through disease. Probably the most common disease causing stenosis of blood vessels is atherosclerosis. Many medical devices and therapeutic methods are known for the treatment of atherosclerotic disease.
Several conditions and diseases are now treatable with stents, catheters, cannulae and other medical devices inserted into the esophagus, trachea, colon, biliary tract, urinary tract and other locations in the body. A wide variety of bioactive materials (drugs, therapeutic agents, diagnostic agents and other materials having biological or pharmacological activity within a patient) have been applied to such medical devices for the purpose of introducing such materials into the patient. Unfortunately, the durable application of bioactive materials to stents and the like, sufficient for such introduction to successfully occur, is often problematic. Moreover, as explained above, the stent itself can cause trauma to the vessel walls, leading in some cases to thrombosis or restenosis.
As an alternative or addition to the use of drug coated or otherwise eluting stents, it is known to use balloon catheters with either a drug coated balloon or with a double balloon structure in which an outer layer is provided with a series of holes through which a drug can pass from an internal chamber of the balloon. The advantage of such drug eluting balloons is that a balloon structure can in some instances cause less trauma to the site being treated and is a temporary mechanism for delivering drugs.
US Publication No. 2003/0032851, for example, discloses a balloon catheter assembly which includes a balloon formed of two layers of non-compliant material which form a chamber for a drug therebetween. The outer balloon is made of a non-compliant material so as to conform to the vessel wall at the treatment site. The catheter element of the assembly includes a lumen for supplying a drug to the chamber formed between the balloon layers.
US Publication No. 2002/0042593 discloses a catheter system having a bulbous or inflatable drug eluting end provided with an outer wall or layer, the outer layer having a series of apertures formed therein. The bulbous end is provided with a bolus of treatment material therein, which can be discharged from the catheter assembly by operation of a pumping mechanism. In one embodiment of the inflatable balloon device disclosed in this document, the cavity within the outer layer of the balloon is loaded with a drug in the uninflated state, and as the balloon is inflated, the drug is discharged through apertures in the outer layer as the inner layer is expanded into the space previously filled with drug.
The above-mentioned devices, while avoiding the use of an implantable device such as a stent for delivery of a medicament, can suffer some disadvantages. For instance, the provision of a chamber within the balloon or other bulbous structure has a size necessarily restricted to the amount of drug to be delivered at least in the first instance during inflation of the balloon. Moreover, the apertures in the outer layer provide an escape path for blood, which must therefore be closed by a suitable valving system, typically provided at a location on the catheter assembly remote from the balloon or other bulbous member. This inevitably results in some blood loss and collection in the catheter assembly.